Our invention relates to a device for generating an electric signal indicative of the variable position of a member capable of either angular or linear displacement relative to means for sensing such displacement. The position signal generator according to our invention lends itself to use for gain control or as a rotary encoder, among other applications.
We know several prior art devices for generating a signal representative of the angular position of a rotary member such as a control knob. Typical of such known devices was a variable resistor comprising a fixed resistive element of arcuate shape across which a constant voltage was to be applied, and a voltage dividing contact movable in sliding engagement with the resistive element. A voltage fraction could be obtained which corresponded to the angular position of the movable contact with respect to the resistive element. Although simple in construction, this known device had the disadvantage that its performance deteriorated with time through abrasion of the resistive element and the movable contact.
Another prior art device employed a rotary disk bearing a series of index marks at constant circumferential spacings. Any angular position of the rotary disk was ascertained on the basis of the number of index marks that were detected from a reference position to the arbitrary angular position of the disk. This second prior art device was also comparatively simple in construction and, being free from relatively sliding parts, defeated the above recited disadvantage of the first recited prior art device. These advantages were offset, however, by the need for initially resetting the disk to the reference position.
The noted weaknesses of the two foregoing prior art devices were absent from still another conventional device that employed a set of concentric rings having discrete conductor regions in preselected angular positions thereof. A plurality of detectors or sensors were provided for detecting the conductor regions on the concentric rings. Various angular positions of the concentric rings were digitally represented by various combinations of binary zero and one outputs from the detectors. We object to this third known device, too, by reason of its bulk as an inevitable result of the use of the concentric rings.